Wind turbines are generally connected to a power grid via a converter, for example, a full scale converter. A 3MW converter typically has a resonance frequency of about 1 kHz. In the absence of a current controller for the converter, a sudden change in the supply voltage to the power grid may excite the resonant mode of a system including the converter, a grid filter and grid impedance (i.e. transformer and line impedance), and may result in high peak transient currents. Such high peak transient currents may activate the converter protection system and may result in unwanted tripping of the wind turbines.
One possible way to mitigate the high transient peak currents is to use passive damping. A shunt damping circuit for the resonant frequency can be placed in parallel with a capacitor connected to the converter and the power grid. However, inductance and capacitance elements of the shunt damping circuit are required to be tuned to the resonant frequency. Energy dissipation occurs with the resistor(s) of the shunt damping circuit.
An alternative way is to use active damping where an output current of the converter is controlled to emulate a current of a damping circuit. However, a high current controller bandwidth is required to control the output current of the converter at the resonant frequency (i.e. about 1 kHz).